Adam Walker (right) with British National party leader Nick Griffin during election campaigning this year, in Barking, east London. Photograph: Paul Hackett/Reuters

A teacher who posted comments on the internet describing some immigrants as "savage animals" and "filth" was cleared of racial and religious intolerance today.

Adam Walker, a British National party (BNP) activist, used a school laptop to claim in an online forum that Britain was a "dumping ground for the filth of the third world".

Walker was a technology teacher at Houghton Kepier Sports College in Houghton-le-Spring, near Sunderland, at the time. He is the first teacher to be brought before the teaching profession's watchdog – the General Teaching Council (GTC) – accused of racial intolerance. He resigned as a teacher in 2007.

The disciplinary panel, made up of three people, said it was "troubled" by Walker's postings but was not satisfied that the "intemperate" views suggested intolerance.

The verdict has renewed calls to ban teachers from being members of the BNP.

Walker, a former soldier, had posted the comments on a forum of Teesside online about the popularity of the BNP in February and March 2007.

Under the pseudonym Corporal Fox, Walker wrote that the BNP had risen in popularity because "they are the only party who are making a stand and are prepared to protect the rights of citizens against the savage animals New Labour and Bliar [sic] are filling our communities with".

The same day he added: "By following recent media coverage of illegal animals and how they are allowed to stay here despite committing heinous crimes, I am, to say the very least, disgusted."

Delivering the committee's verdict, its chair, Angela Stones, said some of Walker's postings contained offensive terms and demonstrated views or an attitude that might be considered racist.

But she said: "The committee does not accept that references to 'immigrants' are of themselves suggestive of any particular views on race. The committee accepts that immigrants to this country come from all over the world. A negative comment about immigration to the UK of itself need not be indicative of racist views or racial intolerance since the race of immigrants is extremely varied.

"For the GTC to prove its case in relation to [the allegation of racial and religious intolerance], the committee has to be satisfied that contributions made by Walker demonstrated views suggestive of racial intolerance.

"Although 'suggestive' may be a relatively low threshold, 'intolerance' is a significant word which the committee has considered very carefully.

"The committee's view is that, to be suggestive of intolerance, the postings would need to deny or refuse to others the right to dissent.

"We do not find that the postings themselves were suggestive of intolerance."

Walker, from Co Durham, was found guilty of making personal use of a school laptop during lessons. This amounts to unacceptable professional conduct, the panel said. They are considering what sanction he should face.

Walker's trade union representative, Patrick Harrington of Solidarity – the Union for British Workers, told the panel that the ex-teacher did not accept his postings were racist and that he had not talked about his political views to pupils or staff. He admitted his views "lacked complexity and balance".

Walker claimed that he had been influenced by media coverage of a female police officer shot dead by two illegal immigrants and the murder of British hostage Kenneth Bigley in Iraq.

"This led me to express intemperate views which lacked complexity and balance," he told the panel yesterday.

"I have never condemned all immigrants or asylum seekers. My comments relate to those I perceive as coming to our country and committing criminal offences or otherwise behaving badly.

"I have certainly never discriminated against an individual on grounds of race, faith or sexuality. Part of why I became a teacher is to help people overcome social disadvantage and reach their full potential."

Bradley Albuery, GTC presenting officer, said the case was not about whether teachers should be allowed to be members of the BNP. "This case is about the actions and behaviour of a registered teacher, using a school property on school premises in school time."

Responding to the news that Walker had been cleared, Chris Keates, general secretary of the NASUWT, the largest teachers' union, said: "This is an absolutely staggering judgment from the GTC.

"The GTC's code of conduct requires teachers to 'demonstrate respect for diversity and promote equality' but the decision today makes a mockery of the code.

"The GTC panel described Walker's comments as 'troubling'. This must go down as a gross understatement. With this decision, the GTC has effectively given a licence to promote religious and racial hatred in schools.

"The NASUWT has been at the forefront of the campaign to ban the BNP and other far right and fascist organisations from working as teachers but we have been badly undermined by this GTC judgment."

Walker has lived in Germany, Cyprus, Egypt and Israel while serving in the armed forces and worked as a teacher in Japan. His wife is Japanese.